Since their initial development in the late 1980's, active-matrix, flat- panel imagers (AMFPIs) have developed at an exponential rate with devices expected soon to reach 30x40 cm2, to exceed 3x10/6 pixels, and with pixel-to-pixel pitches as low as 100 microm. Given the high degree of interest in developing improved means to digitally acquire breast images, it is natural to pose the question: "Is it feasible to develop a practical, full-field, high-resolution (i.e. 50 microm pixel pitch or finer) AMFPI for mammography?" The extrapolation of the design of present AMFPIs (based on either the direct or indirect detection approaches) to 50 microm pitchers of finer is not possible due to a variety of severe difficulties that arise below 100 microm. Consequently, this grant application proposes to test the hypothesis that, through the introduction of fundamental innovations to flat-panel array design, full-field (i.e. 24x30 cm2) direct and indirect detection AMFPIs with spatial resolutions consistent with the rigorous demands of the mammographic application are feasible. an ambitious program of research is proposed involving the iterative design, fabrication, and evaluation (including measurements of observer independent performance variables such as MTF(f), NPS(f) and DQE(f) as well as theoretical modeling based on a cascaded systems approach) of a series of small (approximately 5x6 cm2 with 50 microm to 100 microm pixel pitch) and full-field (24x30 cm2 with 50 mcirom pixel pitch) prototype imagers. A variety of innovations, which will circumvent present limitations in AMFPI design, will be developed and investigated. The successful conclusion of the proposed research will facilitate the creation of new digital mammographic x-ray imaging technologies based on both direct and indirect detection. These technologies will offer 50 microm pixel resolution in the near term, and if required, even finer pixel resolution int he future. Such AMFPIs would offer the promise of digital imaging with large dynamic range allowing wider exposure ranges and significantly reducing the need for retakes compared to screen-film systems. these imagers would be less costly to build them present AMFPIs, and could be packaged with a profile approaching that of a film cassette. They would potentially offer a detective quantum efficiency significantly superior to current screen-film systems allowing for enhanced image quality and/or a reduction in patient exposure and ultimately could serve as a highly useful tool in the early diagnosis of breast cancer.